This invention relates to a four cycle engine and more particularly to an improved cooling structure for the cylinder head of such an engine.
The use of overhead valves is well known in four cycle engines to improve their efficiency and performance. In fact, it is now the practice to employ multiple intake and exhaust valves for the purpose of performance and efficiency improvement. Normally, the intake ports are formed on one side of the cylinder head and the exhaust ports are formed on the other side of the cylinder head. This has the natural tendency to divide the cooling jacket of the cylinder head into a central portion formed above the combustion chamber and between the intake and exhaust ports and side portions positioned outwardly of the respective ports on their sides of the cylinder head. With such an arrangement, it is necessary to insure that there is good flow of liquid coolant between the center and side cooling jacket portions. Furthermore, it is desireable to insure that there will be no areas where the coolant flow is stagnant and wherein air might become trapped. This problem is particularly acute when the engine is provided with non-vertically oriented cylinder bores such as with inclined engines, V-type or opposed engines.
The problem of providing good coolant flow and the avoidance of air pockets in the cylinder head cooling jackets is particularly acute when multiple ports are employed. Where multiple ports are employed, they normally share a common wall that tends to further isolate the side cooling jackets from the center cooling jacket. This can be a particular problem particularly when one of the side cooling jackets is inclined and higher than the central cooling jacket. When this occurs, there is the likelihood that air may be entrapped in this elevated portion of the cooling jacket and cooling efficiency can be significantly deteriorated.
It is, therefore, a principal object to this invention to provide an improved cooling jacket arrangement for the cylinder head of an engine and particularly useful with engines having multiple intake and exhaust ports.
It is a further object to this invention to provide an improved cooling jacket arrangement for an internal combustion engine cylinder head that will insure against the entrapment of air in elevated portions of the cooling jacket.
It is a further object to this invention to provide an improved arrangement for providing water passages between the cylinder head cooling jacket portions that can be easily formed and which will insure good coolant flow and air purging.